Dairy Chemistry, Testing and Analytical Methods
Dairy Chemistry, Testing and Analytical Methods tests proximate analysis, adulteration tests and calculation from analytical readings. The exam expects correct method choice, units and conversion factors.
Core methods
Gerber method measures fat by sulphuric acid digestion and centrifugation; the butyrometer reading is read directly as fat percentage for the specified milk volume. Kjeldahl measures nitrogen; dairy protein is calculated as N × 6.38. Lactose is often measured by Lane-Eynon titration or polarimetry. Ash is measured by incineration. Acidity is titrated and expressed as lactic acid. Freezing point, density and refractive index help detect adulteration.
Worked example
A Gerber butyrometer reading for a milk sample is 4.5. Fat = 4.5%. For 1,000 kg milk, fat mass = 1,000 × 0.045 = 45 kg. For protein, if Kjeldahl nitrogen is 0.55%, protein = 0.55 × 6.38 = 3.51%. Use 6.38 for dairy protein, not the general food factor 6.25.
Traps
Do not read the Gerber fat column at the wrong temperature or ignore the meniscus. Do not use 6.25 for milk protein when the dairy factor is required. Do not confuse titratable acidity with pH. Do not report a result without units or sample basis. Acid digestion in the Gerber test is hazardous; follow safety rules.